Although the proportion of all American families headed by females has increased sharply in the last decade and the family in general is experiencing a "Time of Transition," the female-headed black family is not new. Available data make clear that it was widespread among urban black families for at least 125 years. Our research is designed to determine empirically what led to, sustained and resulted from this particular family form. We focus on the family experience of blacks in late-nineteenth-century Philadelphia. The research is concerned with four general questions: First, was the female-headed black family a cultural "legacy of slavery" or was it a response to particular structural conditions found in the urban environment? Second, if, as we argue, its origins were urban, then what was the "urban component" and how did it induce the adaptation of the female-headed family? Third, can the circularity of argument between poverty and the female-headed family be broken and a clear causal sequence established? Fourth, can factors that set the black experience off from the white -- such as markedly lower fertility, distinct patterns of labor force participation for married women and children and different life course experiences for offspring -- be attributed to the female-headed family? To answer these questions, we draw upon the Philadelphia Social History Project's interdisciplinary research team and its especially rich individual-level data base -- a unique research environment. We adopt a family rather than a household unit of analysis, focus on seven distinct sub-groups within the black population, make comparisons with the Irish, Germans, and native whites, use new mortality data and longitudinal reconstructions of individual and family careers. Testable hypotheses formulated from seven discrete questions about female-headed families are presented in three categories -- Description, Explanation, and Consequence. A detailed discussion is provided of the variety of available micro-level data and of the methodological approaches and statistical techniques selected for implementation.